1. Technical Field
The present invention relates to a gyro vibration piece used in a gyro sensor detecting rotational angular velocity, and to a method of manufacturing the gyro vibration piece.
2. Related Art
A gyro vibration piece according to the related art will be described with reference to FIG. 9. FIG. 9 illustrates an example of a gyro vibration piece, and is a partial plan view of a gyro vibration piece using a crystal. As shown in FIG. 9, a gyro vibration piece 210 includes driving parts 215A and 215C, and a detection part 216A located at a central portion thereof. The driving parts 215A and 215C and the detection part 216A are connected through individual connection parts 221 to a supporting part 212 in an X-Y plane which is a crystalline direction of a crystal. The connection part 221 of the driving parts 215A and 215C is formed in the same manner as the connection part 221 of the detection part 216A, and the connection part 221 of the driving part 215A will thus be described herein. The driving parts 215A and 215C and the detection part 216A are formed in line symmetry with respect to an axis 228 located at a central portion of the supporting part 212 along the X-axis. That is, even though not shown in FIG. 9, a pair of the driving part 215A, a pair of the driving part 215C, and a pair of the detection part 216A are formed with respect to the axis 228. The gyro vibration piece 210 is formed by chemical etching by photolithography. An external shape, an electrode or the like is formed by the chemical etching.
Next, a chemical etching rate will be described. FIG. 10 is a polar coordinate diagram showing the etching rate of a Z-cut crystal substrate in an X-Y plane. Referring to FIG. 10, the etching rate is zero at the center of a circle. In addition, the etching rate becomes higher as it becomes more distant from the center of the circle. It can be understood that the Z-cut crystal has anisotropy in the etching. Particularly, in-plane etching rate become higher in +X direction, +120° direction and −120° direction with respect to the X-axis, while in-plane etching rate become lower in −X direction, +30° direction and −30° direction with respect to the X-axis. On the other hand, the etching rate of Z direction becomes higher in −X direction, +30° direction and −30° direction with respect to the X-axis, while the etching rate of Z direction becomes lower in +X direction, +120° direction and −120° direction with respect to the X-axis.
Due to the anisotropy in the etching, a protrusion-shaped fin 220 is formed on a side of the connection part 221 between the driving parts 215A and 21C and the detection part 212.
Since the fin 220 varies in size depending on the direction of the connection part 221, the driving parts 215A and 215C and the detection part 216A have an asymmetrical shape in width direction, causing the vibration performance of the gyro vibration piece 210 to be deteriorated. Examples of deterioration of the vibration performance of the gyro vibration piece include unstable vibration amplitude due to poor balance of vibration, unnecessary vibration, and the like. Thus, a processing method having a long etching time is employed in order to make the fin as small as possible. As the etching time becomes long, the connection part 221 between the driving parts 215A and 215C and the detection part 216A and the supporting part 212 has a lateral shape formed such that a segment 222 having an angle of +60° (angle ‘a’) and a segment 223 having an angle of 30° (angle ‘b’) are continuously connected to each other. That is, the two segments 222 and 223 are connected to each other by performing an etching process for a long time.
The shape will be described in detail with reference to the driving part. A segment 226 of the driving part 215A and a segment 224 of the supporting part 212 are connected to each other through a segment 222 forming an angle of +60° (angle ‘a’) with respect to X-axis and a segment 223 forming an angle of 30° (angle ‘b’) with respect to X-axis. In addition, a segment 227 of the driving part 215A is connected to a segment of the supporting part 212 in line symmetry to the connection. In addition, a fin 220 is formed almost at a central portion of a thickness direction (Z-axis direction) on the side of the segment 226 of the driving part 215A. Similarly to the driving part 215A, the driving part 215C and the detection part 216A are connected to the supporting part 212 (for example, JP-A-10-96632).
However, in the above-mentioned gyro vibration piece, the segment 226 of the driving part 215A and the segment 224 of the supporting part 212 are connected to each other through the segment 222 forming an angle of +60° (angle ‘a’) with respect to X-axis and the segment 223 forming an angle of 30° (angle ‘b’) with respect to X-axis. In this case, vertices P1, P2, and P3 are formed on portions in which the segments 226, 222, 223, and 224 intersect each other. For example, when an impact, such as dropping, is applied to the gyro vibration piece, stress concentration due to the impact occurs one of the vertices P1, P2, and P3. Due to the stress concentration, the driving parts 215A and 215C, or the detection part 216A may be broken.